Hi!
I have used blind nuts for my models and never had a problem with any of them comming loose. Ca glued of course...easiest way to be certain they stay put!
Never ever use an ordinary bolt and nut to secure a motormount...Its so hard to reach inside the fuselage to hold that nut when fueltank is mounted..and you don't want to remove the tank just because a bolt has come loose ...do you?!

Regards!
Jan K
Sweden